For reference, I also found a pic of 3 different styles of NGK plugs that AndyF put up on another forum at some point. The one on the far left... I had no idea they even made a plug that put the tip that far out there.
Also, IIRC, Andy said he didn't see a discernible difference in performance when he tried the three plugs on an engine dyno. However, I don't know if there was any effort spent looking to re-optimze the ignition timing for each style of plug, either.
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NewbVetteGuy wrote: ↑Mon Aug 02, 2021 1:33 pm
And just to clarify on machining off the first couple of threads on the spark plug, the purpose was to avoid the exposed threads from becoming a hot spot AND to push the spark plug further towards the center of the combustion chamber? (Whole plug extended further into the chamber to go along with the extended tip?)
That's what I would have done for the reason you stated. Here's a pic of an Autolite AR3911 and a Brisk "extra projected" iridium-tip plug. Note the Brisk extends the whole tip and keeps the ground strap length basically standard, rather than extend porcelain, center electrode & ground strap way past the standard config where you end up w/ a very long ground strap.
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Thanks Brad. Those pictures are worth a great many words.
BradH wrote: ↑Tue Aug 03, 2021 11:35 am
However, I don't know if there was any effort spent looking to re-optimze the ignition timing for each style of plug, either.
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Then there's no point in doing the testing. If the purpose is a faster burn then the performance only comes with optimized (reduced) ignition advance.
So tired of seeing ignition system enhancements without increased plug gap and optimized ignition timing. Testing for a decrease in cycle to cycle variations and detonation tendencies would be useful, too, IMHO.
VMC wrote: ↑Tue Aug 03, 2021 11:39 am
I did an A/B test with NGK standard tip and extended tip plugs on a 600+ HP/TQ pump gas 496 with OEM 291 closed chamber rectangle port heads.
Zero difference. Everything was within 2-3 HP/TQ across the board, well within normal testing variances.
Did you recheck / reset ignition advance for best power after switching to extended tip plugs?
Projected-tip spark plug benefits?
Handle a wider operating range and work as well as splitfire BS.
No magic, though rare improvements are measurable, then again like indexing, benefit is random.
Good luck.
BlitzA64 wrote: ↑Fri Jul 30, 2021 2:56 pm
Way back I was racing a class with a 265 Chevy under "stock" rules. I was reading one of the Hot Rod type magazines and there was an article with a 331" Chevy build that was using surface gap plugs that came in Mercury Outboards. The engine picked up power from the usual plugs by moving the spark closer to the center of the chamber. I was getting ready to go to the dyno with my 265 and happened to run across a box of 10 L63y plugs, 1/2" reach rather than 3/8" the same length as the surface gap plugs. I was not allowed to run any ignition but stock points and coil so surface gap may not have worked but these would. Put them in a lathe and turned off the end threads and took them with me. We tuned the engine and had it really good, now was the time. Replaced the plugs and did a pull, a couple hp. started working with timing and got it to 9hp gain! now we are talking about 60 year old chamber shape but 9hp on a 260hp engine was something for a set of plugs.
I guess the moral to the story is there is no real way to tell without testing but that deal sure worked for that engine
Maybe the hp increase you were seeing is because you have moved the spark plug tip further away from the fuel wetting than Darin Morgan shows in his vids?
I've wondered what wet-flow testing would reveal about plug electrode placement in my chamber, too. Darin Morgan's videos on the subject can be quite eye-opening.
As some have pointed out kinda, supposedly idle and part throttle may improve but WOT stays the same pretty much. Dyno can't tell yah how it drives and I've read sim bout some other mods being the same SOP w/o any WOT power improvement.
Are they a tuning crutch?
Does it hurt flow, prob but is that offset by a better burn, maybe that gain just cancels out a flow loss.
If you have more compression or boost you close the gap to make up for the increased air density. So if the fuel mixture is less than WOT do you move the tip closer to improve burn. I noticed the same bout GM moving the vortec plug, they didn't exactly do that for performance. A better burn at part throttle has better fuel economy and that also results in more part throttle power. Vortecs are a great head for street car SOP and also make good performance power But still plenty of aftermarket heads that are better.
